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Nitrogen fixation blog 3

Something to think about that doesn't receive a lot of press and needs more dialogue in the community. Nitrogen is a major component of cellular biomass and is essential for metabolic and cellular functions. Eukaryotic algae, such a Chlorella, Dunellia, Chlamydomonas ect... cannot fix atmospheric nitrogen and thus must reduce Nitrate/Nitrite to ammonia in order to synthesize biomass. Current algal biomass industrial models plan on adding bio-available nitrate or ammonium salts to the culture media. This is fine on a small scale, you just throw in a few grams of "miracle-grow" and the algae go crazy. However, on a large scale one must think about the energy cost of this N fertilization. Atmospheric N gas is in no short supply but the industrial production of ammonia from N gas requires a lot of energy. The Haber process for example, requires temperatures of 500'C and pressures ranging up to 10,000 kilopascales. I'm no chemical engineer nor an economist, but if you need millions of gallons of biodiesel from millions of kgs of biomass then you are going to need a crap load of energetically and economically expensive ammonia. Not to mention that for every unit of energy you put into N fertilization you will effectively loose a unit of energy output from algal fuel production (energy investment vs. payoff). Does anyone know what percentage of algal energy output would go into N-fixation/fertilization using eukaryotic algae? Could you send me a message?

A few solutions:

Many species of photosynthetic cyanobacteria can fix atmospheric nitrogen to ammonia in aerobic environments, like a pond or PBR. This biological process is a wonder of biochemistry, finely tuned over millions of years. The overall rxn uses 16 ATP and 16 electrons to produce two molecules of ammonia and hydrogen gas (both valuable to humans). Heterocystic and mucosol cyanobacteria can run this possess in an aerobic environment by protecting the enzymatic machinery from oxygen poisoning. Thus, engineered oil producing cyanobacteria could be used to efficiently grow energy rich biomass.

Have your heart set (or dollars spent) on eukaryotic algae? It seems possible to co-cultivate eukaryotic algae with N-fixing bacteria in a symbiotic relationship; much like N-fixing leguminous plants (soybeans). There's allot of work to be done here.

Using N rich waste/sewage water or compost "tea" may well be the key. The complex microbial communities associated with sewage and compost, however, add a level of complexity to the already challenging large scale culture of algae - talk about contamination! ughhh
Sat May 08 2010 07:16:53 PM by Prototroph 2763 views

Comments - 3

  • Mahesh wrote:
    Wed May 19 2010 03:57:24 PM

    Can you give more detail about the compost tea?
    How to make it etc

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  • Prototroph wrote:
    Tue August 03 2010 05:39:16 PM

    Sure Mahesh,

    The compost "tea" I refer to here is essentially just compost that has been soaked/brewed/boiled in water. A large amount of water soluble organic macro-molecules and other growth chemicles(like amino-acids, nitrate, amonia, complex vitamins and minerals) are extracted. This is more commonly known as "soil water medium" algae love it and its "100% organic"!

    The compost used is just bacterially digested manure and carbonacious plant waste. The compost, or humus, is realy just a mass of dead bacteria - a treasure trove of bio molecules.

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  • Anand wrote:
    Thu August 05 2010 08:38:49 PM

    Wastewater could be a potential source for microalgae cultivation. The suspended solids are removed my primary treatment, and the BOD (the organic content) is removed through secondary tretment. Water after secondary treatment still contains nitrogen and phosphorus which can be used for growing algae.If the water is discharged to the receiving water bodies without nitrogen and phosphorus removal, it may cause eutrophication which may create a total ecological imbalance to the aquatic life in the waters.
    Algae can be grown in the waters after secondary treatment thus absorbing the nitrogen and phosphorus into biomass and eventually a biofuel. The challenges in this wastewater treatment and algae biomass formation are: contamination by unwanted species like bacteria and of course the cost. Commercially, wastewater treatment using algae is not that successful yet though many attempts have been made.

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